The use of nickel coated heat sinks is common in connection with semiconductor devices. The heat sink is usually of copper or other metal. Frequently, the semiconductor die are attached to the coated heat sinks by soldering. A nickel coating may be applied to the heat sinks by a variety of techniques. Electroless plating is a common method. Electroless nickel layers often contain up to fifteen percent phosphours.
A difficulty which is frequently encountered in soldering semiconductor die to nickel plated heat sinks is the occurrence of voids in the solder. These voids are apparently the result of outgassing which occurs during the soldering process. A further difficulty often encountered in connection with nickel layers is incomplete wetting of the nickel surface by the solder. These problems tend to be more severe with electroless plated nickel layers, particularly those which are high in phosphorus. Thus, a need continues to exist for improved techniques for soldering semiconductor die or other electronic elements to nickel plated or surfaced heat sinks.
Accordingly, it is an object of the present invention to provide an improved process for promoting the solderability of objects coated with nickel.
It is a further object of the present invention to provide an improved process for promoting the solderability of objects coated with nickel which contains phosphorus.
It is an additional object of the present invention to provide a process for improving the solderability of objects coated with electroless nickel plating.
It is a further object of the present invention to provide an improved process for soldering semiconductor die to metal headers having a nickel surface.
It is a further object of the present invention to provide an improved process for reducing void formation in solder joints to phosphorus containing nickel layers or surfaces.